(a) Field of the Invention
This invention relates to novel compounds classified in the field of organic chemistry as phthalazinones, phthalimidines, pyridopyridazinones, and pyrrolopyridinones useful as color-forming substances, particularly in the art of electrochromic recording; to electrochromic recording systems containing as the color-forming substance said phthalazinones, phthalimidines, pyridopyridazinones and pyrrolopyridinones; and to processes for preparing the phthalazinones, phthalimidines, pyridopyridazinones and pyrrolopyridinones.
(b) Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors for electrochromic recording. Among the more important classes, there may be named leuco type dyestuffs such as: phthalides, for example, crystal violet lactone, Malachite green lactone; fluorans, for example, 3-diethylamino-5,7-dimethylfluoran; and indolinobenzospiropyrans, for example, 1,3,3-trimethyl-6'-chloro-8'-methoxyindolinobenzospiropyran. Also utilized as colorless precursors for electrochromic recording, either alone or in admixture with the leuco compounds indicated above, are substances known as redox indicators. The redox indicator which becomes colored or discolored in situ in the electrochromic recording process also is generally a leuco body. Among the types of compounds which are applicable as redox indicators are phenothiazines, for example, leuco methylene blue and benzoyl leuco methylene blue. Other specific indicators are Leucoethyl Nile Blue, Leucomethyl Capryl Blue and Leucosafranine T. Typical of the many such electrochromic recording systems taught in the prior art are those described in U.S. Pat. Nos. 3,726,769, 3,871,972, 3,864,684, 4,017,366, 4,133,933, and U.S. Pat. No. Re. 29,427 which issued Apr. 10, 1973, Mar. 18, 1975, Feb. 4, 1975, Apr. 12, 1977, Jan. 9, 1979, and Oct. 4, 1977, respectively. The methods for electrochromic recording taught in the prior art have many variations. However, basically, one or both sides of a sheet of paper is coated or treated with a coating formulation containing at least one colorless color-forming (leuco) compound. Electrical current is then selectively applied to the coated side of the paper by some means, for example, a stylus or a printing head to which an electrical potential can be applied. The application of the current causes an electrochromic reaction, involving the leuco compound to produce a visible image corresponding to the design traced by the stylus or that of the printing head.
The following items to date appear to constitute the most relevant prior art with regard to the instant invention.
Kuzuya et al. in Chemical Pharmaceutical Bulletin 1980, 28(12), 3561-9 (C.A. 94:141182p) describe the preparation and physical characteristics of 4,4-diaryl-3,4-dihydro-1(2H)-phthalazinones having the structural formula ##STR1## in which R.sub.1 and R.sub.2 are hydrogen or dimethylamino and R.sub.3 is dimethylamino. These phthalazinones are prepared by interacting the corresponding phthalide with hydrazine hydrate in dilute aqueous ethyl alcohol. Although no utility for the compounds is given in the reference, it is taught that the compounds develop a weak green-blue color upon exposure to a weak mineral acid such as dilute hydrochloric acid or to bentonite. It is further stated that upon exposure to a strong acid the phthalazinones are converted to phthalimidines. The phthalazinones are said to show exceptional sensitivity to ultra-violet light and were found to be excellent initiators for photo-polymerization of unsaturated compounds.
Japanese Patent Publication No. 8,089,269, published July 5, 1980, discloses and claims phthalazinones having the structural formula ##STR2## in which R.sup.1 is hydrogen, lower alkylamino, lower alkyl, lower alkoxy or chlorine; R.sup.2 is hydrogen or lower alkyl; and R.sup.3 is lower alkylamino. The compounds are prepared by heating the corresponding phthalide with hydrazine hydrate. These phthalazinones are disclosed as photochemical initiators for photo-polymerization of unsaturated compounds.
U.S. Pat. No. 4,017,366, issued Apr. 12, 1977, discloses and claims a method of printing on thermographic paper according to which the heat for causing the imaging color change in the thermographic coating is generated by means of current in a portion of the coating dampened by a thin film of a conductive salt solution which is dispersed on the thermographic coating. The current is generated by a printing head having spaced electrodes in contact with the dampened portion of the coating.
Japanese Patent Publication No. 51,050,327, published May 1, 1976 discloses phenylhydrazinolactams having the structural formula ##STR3## in which R.sub.1 and R.sub.10 represent hydrogen or lower alkyl; R.sub.2 and R.sub.9 represent hydrogen or lower alkyl; R.sub.3 and R.sub.8 represent lower monoalkylamino, lower dialkylamino, N-phenyl-N-lower alkylamino, dibenzylamino, or N-benzyl-N-lower alkylamino; R.sub.4 and R.sub.7 represent hydrogen, lower alkyl or halogen; R.sub.5 and R.sub.6 represent hydrogen, halogen, lower alkyl or alkoxy; n represents a number from 1 to 4; m represents a number from 1 to 5; X represents hydrogen, halogen, lower alkyl, lower monoalkylamino, lower dialkylamino or acylamino; and Y represents hydrogen, halogen or lower alkyl. The compounds are prepared by heating the corresponding phthalide with phenylhydrazine. No utility is disclosed for the phenylhydrazinolactams.